When you want to quench your thirst on an airplane, make sure the water you get came from a bottle. As the Huffington Post notes, there's a strong likelihood you'll get some pretty bad stuff inside if it was obtained from the tap.

"Do not EVER drink water on an aircraft that did not come from a bottle. Don't even TOUCH IT. The reason being the ports to purge lavatory sh*t and refill the aircraft with potable water are within feet from each other and sometimes serviced all at once by the same guy." —@gruntman

*While the exact water refill process probably varies by airline, the Wall Street Journal ran a test of tap water from 14 different flights in 2002 that found bacteria levels "tens, sometimes hundreds of times above U.S. government limits."